This invention relates to methods and compositions for eliminating or preventing injury to a corn plant caused by the interaction of two or more pesticides applied to the plant in combination, either simultaneously or sequentially. Of particular concern are synergistic responses which occur on a single plant species. Synergistic responses obtained with combinations of herbicides, insecticides and fungicides are described as the combined action of two components of a mixture such that the total effect is greater or more prolonged than the sum of the effects of the two components taken independently.
More particularly, the invention provides methods and compositions for eliminating or preventing injury to a crop plant resulting from the interaction of an organophosphate pesticide and an acetohydroxyacid synthase-inhibiting herbicide. More particularly, this invention relates to methods of and compositions for preventing, inhibiting or ameliorating injury to plants resulting from the interaction of 0,0-diethyl S-[(ethylthio)methyl]phosphorodithioate (phorate) or 0,0-diethyl S-{[(1,1-dimethylethyl)thio]-methyl}phosphorodithioate (terbufos) and a sulfonylurea herbicide such as nicosulfuron or primisulfuron or an imidazolinone herbicide such as imazethapyr, imazamethapyr or imazaquin.
The ever increasing demands for greater quantities and improved quality of food to feed the expanding human population around the world has driven plant science agriculturalists to maximize crop yield and product quality for every hectare of land under cultivation. To this end, knowledgeable farm practitioners have found it advantageous to protect their crops from the time of planting through harvest and beyond against attack, infestation or encroachment by all types of pests including: insects, acarina, bacteria, fungi, nematodes and undesirable plant species. Thus, to achieve the desired protection it has become a rather common practice in the farming industry to use a multiplicity of pest control agents, applied either simultaneously or sequentially, to provide concurrent and continuous protection for the treated crop plant.
In many instances, it has been found that combination treatments afford plant protection against a variety of pests with a single application of combined pesticides or with simultaneous or sequential applications of two or more pesticides applied to the planted and/or growing crop. In practice, there are many known instances of considerable modifications in the biological activity of one pesticide brought about by the prior, simultaneous or sequential application of another pesticide to the same target species. When this occurs it is commonly referred to as an "interaction". As a result of pesticide interactions, adverse effects can occur; and the responses of target species such as corn plants to the combined applications of two or more pesticides are not predictable from the effect of each pesticide applied alone. Said interactions are described as antagonistic when the net effect is a decrease in the biological activity and synergistic when the net effect is an enhancement of biological activity. In other words, a synergistic interaction of a pesticide combination is a more than additive toxic action of two or more pesticides when used together. Pesticide combination applications which result in a synergistic interaction are herein described as synergistic pesticide combinations.
For the past two decades, terbufos and phorate have been used for the control of soilborne pests and as systemic insecticides. These compounds have been used successfully for the control of soilborne and leaf-feeding pests and have been utilized in conjunction with a variety of other pesticides without reports of undesirable interactions. Thus, it is surprising to find that with the recent introduction of certain AHAS inhibiting herbicides (for instance, sulfonylureas such as nicosulfuron and primisulfuron) there appears to be a synergistic interaction observed in corn plants which have been treated at planting with a soil insecticide such as disulfoton, chlorpyrifos, fonofos, phorate or terbufos and thereafter treated early postemergence or when the plants are in the seedling stage, i.e. about the three to five leaf stage, with nicosulfuron or primisulfuron.
It is believed that the synergistic interaction of certain organophosphate compounds with nicosulfuron or primisulfuron occurs when an organophosphate compound is taken into the root system of a plant and inhibits the plant's ability to metabolize the sulfonylurea compound. This inhibition permits the sulfonylurea compound to accumulate in the plant tissue and reach levels which can cause significant injury to the plant.
It is, therefore, an object of this invention to provide methods and compositions for inhibiting, preventing or ameliorating injury to a corn plant resulting from the synergistic interaction of two or more chemicals applied to said plant or the locus in which it is planted or growing.
A further object of this invention is to provide methods and compositions for protecting a corn plant from attack by soilborne pests and preventing incursion into the corn growing area of undesirable plant species while inhibiting or preventing injury to the corn plant due to the synergistic interaction between an organophosphate insecticide and an AHAS-inhibiting herbicide.